Surface modification of WE43 magnesium alloy via alkali/stearic acid treatment for biodegradable drug-eluting stent applications

Abstract

WE43 is a biodegradable magnesium alloy with a high potential for cardiovascular stent applications. Although it has many adequate properties, there are barriers to using it as a drug-eluting stent vehicle. Corrosion and hydrogen gas formation have an adverse effect on the surface, causing attached drug carriers to separate, which limits its functionality as a stent. An alkali treatment in 1 M NaOH solution at various applied potentials was utilized to fix this issue. Subsequently, a stearic acid layer was formed by two different methods to reduce corrosion by decreasing water uptake of the surface. The anodic film's surface morphology and phase structure were analysed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Nanoindentation tests were carried out to evaluate the anodic layer's mechanical properties. Its corrosion behaviour was characterized using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests. The adhesive, thin yet effective oxide layers achieved in all the potentials showed increased corrosion resistance. It significantly decreased hydrogen formation, which were then sealed with stearic acid, and the surface became hydrophobic. This sealing layer acted as an additional barrier and enhanced the corrosion resistance of the magnesium alloy up to fifteen times bigger.